with \(\mathbf {n}\)  the wall normal.
If two squirmers \(i\)  and \(j\) 
are the
collision partners,
which have smooth surfaces so that they do not exchange angular momentum,
their velocities are updated to [1]}
\(\begin{split}\mathbf {V}_i^{\prime } &= \mathbf {V}_i + \delta \mathbf {V}_{ij}, \\\mathbf {V}_j^{\prime } &= \mathbf {V}_j - \delta \mathbf {V}_{ij},\end{split}\) 
